Various types of disease conditions present clinical situations in which a vessel of a patient needs to be artificially supported or held in an open position. For example, blood flow through an artery can be impeded due to a build-up of cholesterol. Also, walls of a vessel may be weakened by an aneurysm.
Intraluminal support frames, sometimes referred to as stents, provide an artificial mechanism to support a body vessel. Generally, these support frames are tubular structures formed in a mesh pattern of metal, plastic, or other suitable material. Self-expanding support frames are able to take on a radially compressed configuration, which facilitates delivery of the frame to the site of interest. Once at the site, the force holding the frame in the radially compressed configuration is removed, and the frame takes on its radially expanded configuration. In this configuration, the frame exerts radially outward force on the vessel, which supports the vessel.
As indicated above, the support frame is typically made of a metal or other suitable material in a mesh-like pattern. While the mesh structure allows for the radial expansion, it concentrates the outward force exerted on the vessel to the individual threads forming the mesh. Little or no force is exerted on the vessel walls in the voids or empty spaces in the mesh structure. As a result, tissue ingrowth can occur in the voids, which may lead to restenosis of the vessel and may necessitate additional treatment for the patient, which might include replacement of the stent.
Several devices have been proposed that combine a graft material with a support frame. The use of a graft provides a continuous surface for supporting the vessel and operates to minimize the ingrowth problem mentioned above.
When compressed, a typical support frame often has a greater length than when it is in its radially expanded configuration. This, in the past, has forced the use of graft materials that can change dimensions along with the support frame. As a result, grafts made of woven and other elastic materials populate the prior art. This placed constraints on the types of graft material that could be utilized. Furthermore, the stretching of the graft material presents an opportunity for kinking, overstretching, and even tearing of the graft.
In view of these and other deficiencies of the prior art, there is a need for an intraluminal graft assembly that allows the support frame to radially expand independently of the graft material.